To assemble or repair large rotary machinery, such as steam turbines, combustion turbines or power generators, it is often necessary to precisely locate a centerline in the machine. Conventional methods for locating a centerline involve the use of a tight-wire. A tight-wire is a steel wire that is strung tightly between two ends of a rotary machine. The wire is stretched across the length of the machine and is then precisely centered at each end to establish the centerline.
Establishing a centerline using conventional tight-wire procedures is labor-intensive and is prone to human error. Positioning a tight-wire at the two ends of a rotary machine requires a large number of measurements and adjustments. The measurements and adjustments must be made in a repetitive and iterative manner to zero in on the centerline. The accuracy of the results are highly dependent upon the operator's expertise. Various adjustment data from wire-sag tables must also be taken into account in order to compensate for the natural sag of the tight-wire.
Another significant problem with conventional tight-wires is the fact that the tight-wire obstructs the internals of a machine during an assembly or repair. While the tight-wire is in place, it is not possible for many other operations to be performed. In industries, like the power generation industry, where every hour of an outage can result in tens of thousands of dollars of lost revenue, this problem is significant. In such industries, it is critical that assembly and repair operations be carefully timed and coordinated to use every available hour of an outage effectively.